Unconsolidated sandstone reservoirs, characterized by low strength, poor cementation, and high velocity sensitivity, are prone to particle migration, which can cause formation damage and reduce production. Frac and pack completions in vertical or directional wells not only control sand and prevent formation damage but also convert near-wellbore radial flow to linear flow. This process reduces fluid velocity around the wellbore, thereby mitigating particle migration and formation damage. This paper aims to optimize fracture half-length in frac and pack operations to both reduce fluid velocity and mitigate particle migration, ultimately improving productivity. Darcy’s law is used to define the radius of particle migration blockage. Then, theoretical models calculate and map fluid velocity distribution under different fracture half-length and reservoir permeabilities, revealing the relationship between fracture half-length and fluid velocity in the reservoir. Based on these results, the fracture half-length is optimized. Numerical reservoir simulations further explore variable-scale frac and pack designs to enhance production in reservoirs with significant vertical heterogeneity. The findings provide a theoretical foundation for optimizing field frac and pack designs in unconsolidated sandstone reservoirs, with the goal of maximizing oil recovery.